Optical semiconductor relay

ABSTRACT

An optical semiconductor relay comprises a light emitting element converting an electrical signal into an optical signal, a first photodiode array receiving the optical signal from the light emitting element. The first photodiode array converts the optical signal into an electrical signal. The relay is further provided with a first diode having one electrode connected to one end of the first photodiode array and a MOSFET. The MOSFET has a gate terminal connected to other electrode of the first diode, and a source terminal connected to other end of the first photodiode array. A second photodiode array is arranged to receive the optical signal from the light emitting element. The second photodiode array converts the optical signal into an electrical signal and has both ends connected to the respective electrodes of the first diode. A control circuit connected between the gate and source terminals of the MOSFET.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims the benefit of priorityfrom the prior Japanese Patent Application No. 2002-273500, filedSeptember 19th 2002, the entire contents of which are incorporatedherein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to an optical semiconductor relay,and more particularly, to an optical semiconductor relay designed toreduce switching time.

BACKGROUND OF THE INVENTION

[0003] An optical semiconductor relay is generally provided with aninput light emitting element such as an LED (hereinafter, referred to asLED), an output photodiode array (hereinafter, referred to as PDA) and aswitching MOSFET. The PDA receives input light from the LED and convertsthe light into a voltage. This voltage becomes a gate voltage of theswitching MOSFET, and the optical semiconductor relay performs theswitching by driving the MOSFET. Since electrical signals are convertedinto light to be transmitted, it is possible to insulate between theinput and output electrically. At the same time, it is possible to drivea small-size optical semiconductor relay with low power consumption athigh speed without contact wear, unlike a mechanical relay.

[0004] An optical semiconductor relay is disclosed in U.S. Pat. No.5,013,926 (FIG. 4). FIG. 1 shows the circuit structure of such anoptical semiconductor relay. As shown in the FIG. 1, an anode end of afirst PDA 2 which receives light from an LED 1, a diode 5 and a gateterminal of a MOSFET 4 are connected in series. A cathode end of thefirst PDA 2 is connected to the source terminal of a MOSFET 4. The anodeend of first PDA 2 is connected to a cathode end of a second PDA 3, andan anode end of second PDA 3 is connected to a cathode electrode ofdiode 5 through an impedance element 10. First PDA 2 and second PDA 3have a plurality of photodiodes respectively the same polarities ofwhich are connected in series. Connection area of the photodiodesconstituting the second PDA 3 is smaller than those of first PDA 2.First PDA 2 and second PDA 3 are connected in series as a whole.

[0005] A normally-on transistor (hereinafter, referred to as J-FET 12)constituting a control circuit with impedance element 10 is connected asto enclose impedance element 10 by the gate and source terminalsthereof. The control circuit controls speed and photosensitivity of theoptical semiconductor relay by controlling charging and discharging timeof the switching MOSFET constituting the optical semiconductor relay.

[0006] In this optical semiconductor relay, when an input electricalsignal is turned on (ON-state), LED 1 emits light, and first PDA 2received this light converts the light into an electrical signal.Current flows to the gate terminal of MOSFET 4 through diode 5, and thegate of MOSFET 4 is charged and shifted to an ON-state. Meanwhile, partof current converted at first PDA 2 is supplied to the gate terminal ofJ-FET 12 through impedance element 10. Second PDA 3 also receives thelight from LED 1 and generates a current. This current is supplied tothe gate terminal of J-FET 12 with the current converted at first PDA 2.A potential difference between both ends of impedance element 10 isapplied between the gate and source of J-FET 12 as a bias voltage, J-FET12 is shifted to an OFF-state.

[0007] When the input electrical signal is turned off (OFF-state), theoptical signal is not output from LED 1, and the electrical signals fromfirst PDA 2 and second PDA 3 is not output either. Accordingly, thecurrent vanishes, and the bias voltage of J-FET 12 becomes 0 volt. Thus,J-FET 12 is shifted to an ON-state. When J-FET 12 shifts to an ON-state,it is short-circuited between the gate and the source of MOSFET 4.Therefore, a stored electric load is quickly discharged, and MOSFET 4 isshifted to an OFF-state.

SUMMARY OF THE INVENTION

[0008] An optical semiconductor relay according to an embodiment of thepresent invention comprises: a light emitting element converting anelectrical signal into an optical signal; a first photodiode arrayreceiving the optical signal from the light emitting element, the firstphotodiode array converting the optical signal into an electricalsignal; a first diode having one electrode connected to one end of thefirst photodiode array; a MOSFET having a gate terminal connected toother electrode of the first diode, and a source terminal connected toother end of the first photodiode array; a second photodiode arrayreceiving the optical signal from the light emitting element, the secondphotodiode array converting the optical signal into an electricalsignal, and having both ends connected to the respective electrodes ofthe first diode; and a control circuit connected between the gate andsource terminals of the MOSFET.

[0009] An optical semiconductor relay according to another embodiment ofthe present invention comprises: a light emitting element converting anelectrical signal into an optical signal; a first photodiode arrayreceiving the optical signal from the light emitting element, the firstphotodiode array converting the optical signal into an electricalsignal; a first diode having one electrode connected to one end of thefirst photodiode array; a MOSFET having a gate terminal connected toother electrode of the first diode, and a source terminal connected toother end of the first photodiode array; a second photodiode arrayreceiving the optical signal from the light emitting element, the secondphotodiode array converting the optical signal into an electricalsignal, and having one end connected to one electrode of the firstdiode, and other end connected to other electrode of the first diodethrough an impedance element; a normally-on transistor having source anddrain terminals connected to the gate and source terminals of theMOSFET, respectively, and a gate terminal connected to a connectionpoint between the impedance and the second photodiode array; and abypass diode connected to the impedance element in parallel.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a view showing a circuit structure of a conventionaloptical semiconductor relay.

[0011]FIG. 2 is a view showing a circuit structure of an embodiment ofan optical semiconductor relay of the present invention.

[0012]FIG. 3 is a view showing a specific circuit structure of FIG. 2.

[0013]FIG. 4 is a view showing a circuit structure of another embodimentof an optical semiconductor relay of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0014] A first embodiment in accordance with the present invention willbe explained with reference to FIG. 2 and FIG. 3.

[0015]FIG. 2 is a circuit diagram of an embodiment of an opticalsemiconductor relay of the present invention. As shown in the FIG. 2, afirst photodiode array (a first PDA 2) is provided to optically couplewith a light emitting element (an LED 1). The light emitting elementconverts an electrical signal into an optical signal. The firstphotodiode array receives the optical signal from the light emittingelement and converts the optical signal into a first electrical signal.A cathode end of first PDA 2 and a source terminal of a switching MOSFET4 are connected. An anode end of first PDA 2 is connected to a gateterminal of MOSFET 4 through a first diode 5 in series. An anodeelectrode of diode 5 is connected to the anode end of first PDA 2, and acathode electrode of diode 5 is connected to the gate terminal of MOSFET4.

[0016] A second photodiode array (a second PDA 3) having a smallerconnection area than that of first PDA 2 is provide to increase outputvoltage. A second photodiode array receives the optical signal from thelight emitting element and converts the optical signal into a secondelectrical signal. An anode end of first PDA 3 is connected to the gateterminal of MOSFET 4 substantially without an impedance element, and acathode end of second PDA 3 is connected to the anode end of first PDA2. First PDA 2 and second PDA 3 are connected in series as a whole. Thecathode end of second PDA 3 is connected to the anode end of first diode5. The anode end of second PDA 3 is connected to the cathode end offirst diode 5. A control circuit 6 is connected between the gate andsource terminals of MOSFET 4.

[0017]FIG. 3 shows a specific circuit structure of the opticalsemiconductor relay, including the structure of control circuit 6. Animpedance element 7 (e.g., resistor), an NPN transistor 8 and a seconddiode 9 constitute control circuit 6. Impedance element 7 is connectedbetween the gate and source terminals of MOSFET 4 and the cathodeterminal of first PDA 2. A base and collector terminals of NPNtransistor 8 are connected to both ends of impedance element 7,respectively. Diode 9 is connected between an emitter and base terminalsof NPN transistor 8. An anode electrode of diode 9 is connected isconnected to the emitter terminal of NPN transistor 8.

[0018] According to this circuit structure, when a signal is inputted, acurrent produced by first PDA 2 flows from first PDA 2 to the gate ofMOSFET 4 through diode 5, and a current produced by second PDA 3 flowsfrom second PDA 3 to the gate of MOSFET 4. Thus, the gate of MOSFET 4 isshifted to an ON-state. In these paths, charging resistance becomesextremely small since an impedance element does not exist substantially.Thus, MOSFET 4 is turned on swiftly.

[0019] When a signal is inputted, NPN transistor 8 constituting controlcircuit 6 is turned off because a current flowing from the anode of thediode 9 to the cathode thereof makes a voltage between the base andemitter reversely biased. On the other hand, when a signal is notinputted, an electric charge stored in the gate of MOSFET 4 isdischarged to the base terminal of NPN transistor 8 through impedanceelement 7. The electric charge becomes a base current. Thus, NPNtransistor 8 is shifted to an ON-state.

[0020] By employing control circuit 6, the impedance element is notconnected in series with respect to the charging current of MOSFET 4.Accordingly, control circuit 6 does not act as charging resistance, andthe switch-on time of the optical semiconductor relay can be reduced. Atthe same time, NPN transistor 8 and diode 9 can be formed in a spacewhich is one-tenth or less of the space required for the normally-ontransistor (hereinafter, J-FET: junction FET transistor). Thus, it ispossible to shrink chips and reduce manufacturing costs.

[0021] A second embodiment in accordance with the present invention willbe explained with reference to FIG. 4.

[0022]FIG. 4 is a circuit structure of another embodiment of an opticalsemiconductor relay of the present invention.

[0023] As shown in the drawing, an anode end of a first PDA 2 whichreceives light from an LED 1, a diode 5 and a gate terminal of a MOSFET4 are connected in series, and a cathode end of the first PDA 2 isconnected to the source terminal of a MOSFET 4. The anode end of firstPDA 2 is connected to a cathode end of a second PDA 3, and an anode endof second PDA 3 is connected to a cathode electrode of diode 5 throughan impedance element 10(e.g., resistor). First PDA 2 and second PDA 3are a plurality of photodiodes of which the same polarities areconnected in series. Connection area of the photodiodes constituting thesecond PDA 3 is smaller than those of first PDA 2. First PDA 2 andsecond PDA 3 are connected in series as a whole.

[0024] A normally-on transistor (hereinafter, referred to as J-FET 12)constituting a control circuit with impedance element 10 is connected asto enclose impedance element 10 by the gate and source terminalsthereof. The control circuit controls speed and photosensitivity of theoptical semiconductor relay by controlling charging and discharging timeof the switching MOSFET constituting the optical semiconductor relay. Aplurality of serially connected diode elements (hereinafter, referred toas bypass diode 11) are connected to impedance element 10 in parallel.

[0025] A transistor which turns off at 1 to 2 volts is usually employedfor J-FET 12. When a potential difference between both ends of impedanceelement 10 exceeds 2 volts and J-FET 12 is turned off, bypass diode 11is operated. Consequently, serial impedance of second PDA 3, serving ascharging resistance, is reduced, and the switch-on time of the opticalsemiconductor relay is shortened.

[0026] The conventional optical semiconductor relay has had a problemthat a charging time is delayed, in other words, a switch-on time isincreased. It is because an impedance element acts as chargingresistance since the impedance element constituting a control circuit isconnected in series with respect to a charging current flowing from asecond PDA to a MOSFET.

[0027] According to the embodiments of the present invention, it ispossible to provide an optical semiconductor relay capable of shorteningthe switch-on time without degrading the operation functions, andshrinking chips and reducing manufacturing costs.

[0028] The present invention is not limited to the embodiments describedabove. For example, a PNP transistor may be employed instead of NPNtransistor 8 shown in FIG. 3. An infinitesimal impedance for adjustingswitching time or photosensitivity may be inserted between second PDA 3and MOSFET 4.

[0029] Other embodiments of the present invention will be apparent tothose skilled in the art from consideration of the specification andpractice of the invention disclosed herein. It is intended that thespecification and example embodiments be considered as exemplary only,with a true scope and spirit of the invention being indicated by thefollowing.

What is claimed is:
 1. An optical semiconductor relay comprising: alight emitting element converting an electrical signal into an opticalsignal; a first photodiode array receiving the optical signal from thelight emitting element, the first photodiode array converting theoptical signal into an electrical signal; a first diode having oneelectrode connected to one end of the first photodiode array; a MOSFEThaving a gate terminal connected to other electrode of the first diode,and a source terminal connected to other end of the first photodiodearray; a second photodiode array receiving the optical signal from thelight emitting element, the second photodiode array converting theoptical signal into an electrical signal, and having both ends connectedto the respective electrodes of the first diode; and a control circuitconnected between the gate and source terminals of the MOSFET.
 2. Theoptical semiconductor relay according to claim 1, wherein the controlcircuit comprises: an impedance element connected between the gate andsource terminals of the MOSFET; a bipolar transistor having base andcollector terminals connected to both terminals of the impedanceelement, respectively; and a second diode connected between an emitterand base terminals of the bipolar transistor.
 3. The opticalsemiconductor relay according to claim 1, wherein a plurality ofphotodiodes of a same polarity are connected in series in each of thefirst and second photodiode arrays, and the photodiodes constituting thefirst photodiode array has connection areas larger than those of thephotodiodes constituting the second photodiode array.
 4. The opticalsemiconductor relay according to claim 1, wherein an anode electrode ofthe first diode is connected to an anode end of the first photodiodearray.
 5. The optical semiconductor relay according to claim 2, whereinthe impedance element is a resistor.
 6. The optical semiconductor relayaccording to claim 2, wherein an anode of the second diode is connectedto the emitter terminal of the bipolar transistor and the sourceterminal of the MOSFET, and a cathode of the second diode is connectedto a cathode end of the first photodiode array.
 7. An opticalsemiconductor relay, comprising: a light emitting element converting anelectrical signal into an optical signal; a first photodiode arrayreceiving the optical signal from the light emitting element, the firstphotodiode array converting the optical signal into an electricalsignal; a first diode having one electrode connected to one end of thefirst photodiode array; a MOSFET having a gate terminal connected toother electrode of the first diode, and a source terminal connected toother end of the first photodiode array; a second photodiode arrayreceiving the optical signal from the light emitting element, the secondphotodiode array converting the optical signal into an electricalsignal, and having one end connected to one electrode of the firstdiode, and other end connected to other electrode of the first diodethrough an impedance element; a normally-on transistor having source anddrain terminals connected to the gate and source terminals of theMOSFET, respectively, and a gate terminal connected to a connectionpoint between the impedance and the second photodiode array; and abypass diode connected to the impedance element in parallel.
 8. Theoptical semiconductor relay according to claim 7, wherein thenormally-on transistor is a junction FET transistor.
 9. The opticalsemiconductor relay according to claim 7, wherein the impedance elementis a resistor.
 10. The optical semiconductor relay according to claim 7,wherein the bypass diode is a plurality of diode elements connected inseries.